When a speech/audio signal is transmitted in a packet communication system typified by Internet communication, a mobile communication system, or the like, compression/encoding technology is often used in order to increase speech/audio signal transmission efficiency. Also, recently, there is a growing need for technologies of simply encoding speech/audio signals at a low bit rate and encoding speech/audio signals of a wider band.
Various technologies of integrating plural coding technologies in a hierarchical manner have been developed for the needs. For example, Non-Patent Literature 1 disclosed a technique of encoding a spectrum (MDCT (Modified Discrete Cosine Transform) coefficient) of a desired frequency band in the hierarchical manner using TwinVQ (Transform Domain Weighted Interleave Vector Quantization) in which a basic constituting unit is modularized. Simple scalable encoding having a high degree of freedom can be implemented by common use of the module plural times. In the technique, a sub-band that becomes a coding target of each hierarchy (layer) is basically a predetermined configuration. At the same time, there is also disclosed a configuration in which a position of the sub-band that becomes the coding target of each hierarchy (layer) is varied in a predetermined band according to a characteristic of an input signal.